A mechanical seal is used for sealing by utilizing a sliding contact between a rotating ring rotating with a rotating shaft and a stationary ring non-rotatably held by a seal housing. The stationary ring needs to be arranged in a narrow space within the seal housing of the rotating machine and is thus subject to constraints on layout and installation. Thus, when the stationary ring is used under a high pressure and a high temperature, the stationary ring may be affected by an irregular internal stress caused by a pressure from a sealed fluid or an irregular internal stress caused by heat of the sealed fluid or sliding heat. In order to prevent influences from such irregular internal stresses, the mechanical seal of an intermediate ring-mediated type, in which an intermediate ring is interposed between the rotating ring and the stationary ring, is used.
As exemplified in Patent Citation 1, the mechanical seal of an intermediate ring-mediated type is mainly configured from a rotating ring fixed on a rotating shaft and rotating with the rotating shaft, a stationary ring held by a seal housing in an axially movable manner, the stationary ring being biased toward the rotating ring side by a spring, and an intermediate ring arranged between the rotating ring and the stationary ring, the intermediate ring being loosely fitted with a pin projected from the stationary ring and held in a relatively non-rotatable manner in a state in which a relative displacement within a predetermined range in an axial direction and in a radial direction is allowed. As a structure of the mechanical seal, annular protrusions are formed on both sides of the intermediate ring in a substantially symmetric manner. In this structure, a sliding surface, which makes a sliding contact with a side surface of the rotating ring, is arranged on a tip end of the annular protrusion at a rotating ring side, and a sealing surface, which makes a contact with a side surface of the stationary ring to seal inside and outside sections in the radial direction, is arranged on a tip end of the annular protrusion at a stationary ring side.